A method (hereinafter referred to as the “oil reservoir method”) in which sliding parts are lubricated by oil pooled in a crankcase is widely used as the lubricating method for an engine. Engines that use the oil reservoir method are mounted in work machines.
In oil-reservoir engines, the pooled quantity of oil, i.e., the oil level, must be at a suitable level for the sliding parts to be smoothly lubricated. Japanese Patent Post-Exam Publication No. 53-44615 (JP-53-44615B) and Japanese Laid-Open Patent Publication No. 2004-150374 (JP-2004-150374A) disclose oil level detectors that detect the oil level.
The oil level detectors disclosed in JP-53-44615B and JP-2004-150374A are mounted in vehicle engines and are provided with a float switch. In these oil level detectors, the float drops in accordance with the reduced oil level when the oil level has decreased to a fixed lower-limit level. Therefore, the reduced level can be detected when the switch senses that the float has dropped.
When the oil level detector disclosed in JP-53-44615B detects that the level has dropped, a lamp, a buzzer, or another warning device emits an alarm.
The oil level detector disclosed in JP-2004-150374A, on the other hand, constantly detects the state of the road surface on which the vehicle is traveling, and stops detecting the oil level when the condition of the road surface is determined to be poor. As used herein, the phrase “poor condition of the road surface” refers to a condition in which the road surface negatively affects oil level detection because the surface of the oil is considerably agitated or sloped.
Specifically, the oil level detector disclosed in JP-2004-150374A emits an alarm when the detector has detected that the oil level has dropped in cases in which (1) the condition of the road surface is good, and temporarily suspends oil level detection to prevent the detector from emitting an alarm in cases in which (2) the condition of the road surface is poor. For this reason, the detector can be prevented from accidentally detecting that the oil level has dropped when the road surface condition is poor.
Some of the engines mounted in work machines are multipurpose engines. Some of the work machines produce severe vibrations, and in some work machines the orientation of the multipurpose engine can be temporarily tilted at a considerable angle. Thus, there are multipurpose engines that are used in harsher environments than those mounted in a vehicle. In spite of this fact, when the oil in the crankcase is sufficiently pooled, sliding parts can still be smoothly lubricated with the oil even if the surface of the oil has considerably fluctuated or has been temporarily set at an angle.
It has been proposed to provide the oil level detectors disclosed in JP-53-44615B and JP-2004-150374A to multipurpose engines used in such harsh environments. However, the oil level detectors disclosed in JP-53-44615B and JP-2004-150374A merely emit an alarm when the oil level has dropped.
In contrast, stopping the engine to more positively respond to the situation in which the oil level has dropped can be considered in order to improve the durability of the engine. Specifically, when oil is insufficient at engine startup, startup is prevented, and when oil is insufficient during engine operation, the engine can be stopped.
In this case, however, an engine in which oil is sufficiently pooled in the crankcase would still stop when the surface of the oil severely and considerably fluctuates during work, or when the oil detector detects that the oil level has dropped when the engine is temporarily tilted. As a result, work would have to be suspended. The work efficiency of a work machine can therefore be improved.
In view of the above, there is a need for a technique that assures the durability of a multipurpose engine mounted in a work machine which produces severe vibrations, or a work machine which performs work temporarily tilted at a considerable angle, and that can improve the work efficiency of a work machine in, which a multipurpose engine is mounted.